The present invention relates to the manufacture of integrated circuits on a substrate. More particularly, the invention relates to a method and apparatus for improved plasma deposition of layers on substrates.
One of the primary steps in the fabrication of modem semiconductor devices is the formation of a thin layer on a semiconductor substrate by chemical reaction of gases. Such a deposition process is referred to generally as chemical-vapor deposition (xe2x80x9cCVDxe2x80x9d). Conventional thermal CVD processes supply reactive gases to the substrate surface where heat-induced chemical reactions take place to produce a desired layer. Plasma-enhanced CVD (xe2x80x9cPECVDxe2x80x9d) techniques, on the other hand, promote excitation and/or dissociation of the reactant gases by the application of radio-frequency (xe2x80x9cRFxe2x80x9d) energy to a reaction zone near the substrate surface, thereby creating a plasma. The high reactivity of the species in the plasma reduces the energy required for a chemical reaction to take place, and thus lowers the temperature required for such CVD processes as compared to conventional thermal CVD processes. These advantages are further exploited by high-density-plasma (xe2x80x9cHDPxe2x80x9d) CVD techniques, in which a dense plasma is formed at low vacuum pressures so that the plasma species are even more reactive. xe2x80x9cHigh-densityxe2x80x9d is understood in this context to mean having an ion density that is equal to or exceeds 1011 ions/cm3.
Particular applications that lend themselves to effective use of HDP-CVD techniques include shallow-trench isolation (xe2x80x9cSTIxe2x80x9d), premetal dielectric (xe2x80x9cPMDxe2x80x9d) applications, and intermetal dielectric (xe2x80x9cIMDxe2x80x9d) applications. One issue that affects deposition properties in various such applications is diffusion between adjoining layers that have different compositions, which can adversely affect certain desired properties of the resulting layer structure. One approach that has been used to prevent such diffusion includes deposition of an additional intermediate barrier layer. For example, when doped silicon oxide is deposited in IMD applications, diffusion of the dopant to metal lines may cause the formation of undesirable chemical species at the oxide/metal interface, resulting in poor adhesion between the oxide and the metal. Deposition of a silicon-rich liner on the metal prior to depositing the doped silicon oxide layer acts to prevent dopant diffusion. Including the barrier layer has the beneficial effect of improving adhesion in the structure.
It is almost routine now in many applications to deposit barrier layers when forming certain structures. For example, a silicon-rich oxide liner is commonly formed on a substrate prior to deposition of a layer of fluorine-doped silicon oxide in fluorosilicate-glass (xe2x80x9cFSGxe2x80x9d) applications using HDP-CVD. Although this has numerous advantages over comparable applications that do not use a silicon-rich oxide liner, significant variation is still seen in the composition of the liner so that its beneficial effects are not uniformly available. Furthermore, this composition variation has specific characteristics peculiar to individual deposition chambers. Mass production of integrated circuits would be improved with a technique that produces improved composition uniformity, without affecting the vagaries of individual deposition chamber configurations.
Embodiments of the invention are directed to a method and system for forming a layer on a substrate in a process chamber. Deposition gases are provided to the process chamber and permitted to mix in the desired relative concentrations prior to the deposition step, resulting in improved composition uniformity of the layer. In certain embodiments, two distinct plasmas are used, a first to heat the substrate and a second that is used for the actual deposition.
Thus, in various embodiments, a first gaseous mixture is provided to a process chamber. A first plasma is generated from the first gaseous mixture to heat the substrate. The plasma is then terminated and a second gaseous mixture is provided to the process chamber such that the second gaseous mixture is substantially uniformly mixed. A second plasma is then generated from the second gaseous mixture to deposit the layer on the substrate. In certain embodiments, the first gaseous mixture consists of oxygen or comprises both oxygen and argon. To deposit a silicon-rich oxide layer, the second gaseous mixture may comprise oxygen and silane. In one embodiment the concentration ratio between the oxygen and silane is between 0.5 and 1.5. In another embodiment, the second plasma is a high-density plasma and may be generated by initiating a low-pressure strike of the second gaseous mixture.
The methods of the present invention may be embodied in a computer-readable storage medium having a computer-readable program embodied therein for directing operation of a substrate processing system. Such a system may include a process chamber, a plasma generation system, a substrate holder, a gas delivery system, and a system controller. The computer-readable program includes instructions for operating the substrate processing system to form a thin film on a substrate disposed in the processing chamber in accordance with the embodiments described above.